Telegraphy.



Patented Aug. 26, I902. A. G. CREHORE.

TELEGBAPHY.

(Application filed Oct. 21, 1901.)

3 Sheets-8haat -I.

(No Model.)

lm/4714009 co No. 707,830. Patented Aug. 26, I902.

A. G. CREHORE.

TELEGRAPHY.

I'Applicaticm filed Oct. 21, 1901.) (,No Model. 3 Sheefs$heet2.

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Patented Aug. 26, I902. A. C. CREHORE.

TELEGBAPHY.

(Application filed Oct. 21, 1901.

3 Sheets-Sheet 3.

(No Model.)

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TH: NORRIS PETE-KS co. mo'rmur hmq wasnmc'rou u c UNTT D STATES PATENT OFFICE.

ALBERT Cl CREHORE, OF TARRYTOWN, NEW YORK.

TELEGRAPHY.

SPECIFICATION forming part of Letters Patent No. 707,830, dated August 26, 1902. A Application filed October 21, 1901- Serial No. 79,387. (No model.) i

To aZZ whom, 7215 may concern.-

Be it known that I, ALBERT G. CREHORE, a citizen of the United States, and a resident of Tarrytown, in the county of WVestchester and State of New York, have invented certain new and useful Improvements in Telegraphy, of which the following is a specification.

My invention relates to that class of telegraphs known as superposed-current telegraphs, wherein the capacity of the line is increased by transmitting one class or set of signals over said line by means of momentary currents of short duration and sharply defined or having a high rate of electromotiveforce change superposed upon currents having a slower rate of change and, generally speaking, of longer duration,wh-ich latter cur rents will be hereinafter termed for brevity continuous currents, while the portion of apparatus through which signals are transmitted by currents of the latter character will be termed hereinafter the continuous-current side of the system.

As myinvention has a large field of utility in connection with circuits wherein the continuous currents are employed in connection with Morse telegraph apparatus, I shall hereinafter describe myinvention as carried out in connection with the Morse telegraphline. It will also be assumed in the following description that the duration of each signal is determined by the length of time during which a succession of pulsatory currents flows, although, as well understood in the art, the transmission of signals on the pulsatorycurrent side of a superposed-current tele graph may be effected by the use of two pulsations separated by a space of time during which no pulsations flow, a single pulse marking the beginning and another pulse the end of the signal or character.

Telegraphs of this general class have never proved entirely satisfactory in operation, and

- a great source of difficulty has been the fact that the distributed capacity of the line has the effect ofcausing the pulsatory currents to decrease rapidly from the transmitting end or point where the source of pulsations is located to the receiving end of the line, and in order to maintain the necessary current at the receiver end for operating the receiver it is necessary to employ currents which become rapidly larger as the productof the resistance and the distributed capacity of the line increases; but if the pulsatory current exceeds a certain value there will be interference with the continuous-currentrelay on accountofthe proportion of total current passing therethrough. Moreover, the presence of the necessary condenser-shunts in such systems introduces another disturbing factor, because the larger the current the greater the reaction of the condenser and consequent tendency of the same to disturb the working of the other parts of the system. If there were no distribu ted capacity to the line, it would be possible by raising the voltage to produce the desired current at the distant end, and the current at the transmitting end would then he the same as at the receiving end, even though there are a large number of intermediate stations; but if there is distributed capacityalong the line between each station, as in practice, this causes the transmitting-current to increase and the received current to decrease at a surprising rate, so that the maximum allowable current falls below the re quired limit.

One of the purposes of my present invention is to increase the limit of pulsatory current which it is permissible to use, thereby increasing the length of line or the number a large number of condensers to the Morse line will have less disturbing influence on the Morse working, while, moreover, the cost of equipment of the line is very considerably reduced. This freedom from disturbance is an especially important factor when the coudenser inquestion is in the shuntaround the Morse key, since the practicable limit of condenser capacity which may be used in this location. without detection .by the operator through its disturbing efi'i' ect isvery small. Again, the ability to use a smaller condenser according to my invention is of valuein permitting currents of lower frequency to be used upon the line, and hence the system may be worked with less tendency to inductive disturbances upon neighboring lines.

wave form and in the various condensershunts used in the system a suitable value ofinduetance or reactance adapted to balance as near as may be the impedance of the condenser, as hereinafter described. Pulsatory systems as heretofore organized have general lyem ployed pulsatory generators depending upon the making and breaking of circuits containing ind u'ction-coils and batteries. The pulsations thus produced depart considerably from a sine wave, and hence .the use in such systems of a balancing-coil or reactance would V be of practically little good, since waves ditfering from'a sine wave do not, either theoretically or practically, permit the impedance of the condenser to be balanced or reduced by the interposition of inductance. In practice the inductance which furnishes the reactance for balancing the reactance of the condenser may be afforded in some cases by coils of electromagnets employed for a receiving part of the systemas, for instance, by the coils for the pulsatory-current receiver as would be the case where said receiver is in a condenser-shunt around the continuous; current receiver or other portion ofthe circuit having suitable inductance. In this case 7 it is obvious that the receiver-coils will be prefer-ably wound with the proper numberof turns of wire to give them the necessary reactance. In other cases, as when the receiver for the pulsatory-current side of the system is in other relation to the circuit, a supplemental inductance or'reactance balancing or counteracting the condenser-reactance would be-used in the shunt-circuit with the condenser and-whether said shunt be around the continuous-current receiveral'one or the'continuous-current transmitter alone, or both. Theinductance may-be furnished by any form of coil; butin general I'prefer to employ a special form of'inductance-coil. It is difiicult in practice to approximate the theoretical balance, because the theory neglects the losses whichare necessarily involved when any coil isemployed. Thelossinthecondenserisquite small and may beordinarily neglected, and it might seem, given the problem of finding a coil to balance three microfarads at one hun dred and fifty cycles, easy to find'a coil which would reduce the condenser-shunt to a few ohms. Tobalance three microfarads at one hundred-and fit'ty cycles requires an inductance of about .37 henries; but trials such as I have made have resulted at the best in securing a condenser-shunt measuring'not less than one hundred and ten ohms. In practice vrents sufficiently constant in value.

one hundred and twenty-five ohms will do, which is still a great advantage in the operation of the system over a shunt which with the condenser-line would be,'say, three hundred and fifty-four ohms. The coils might be made by winding insulated wire in a coil of sufficient size to produce the required reactance without iron; but this, would not be desirable, because the resistance of the coil and the amount of copper required would be too large. If-the coil is wound upon an iron core, the size may be greatly reduced for the same reactance, and if the magnetic circuit of the core is completely closed by iron the largest reactance may be produced with a given quantity of iron and copper. parent resistance of such a coil for alternating currents is much greater than its ohmic resistance for direct currents and depends largely upon the amount of iron used.

For the purpose of a balancing reactance employed in a system of telegraphy in the manner above described it is desirable that the coils should maintain their values of apparent resistance and reactance as nearly con-. stant as possible for all values of working current. Moreover, while furnishing the required fixed reactance to counterbalance the given condenser at a determined frequency they should also have a comparatively low apparent resistance. These conditions cannot all be satisfactorily attained in the forms of reactance just mentionedfor instance, the closed-magnetic-circuit type of coil does not maintain the apparent resistance and reactance for diiferent values of working cur- An in ductance consisting of a coil wound on a straight iron core while it in a measure satisfies the requirement of constant resistance and reactance for all values of working current requires an undue amount of material. I find, however, that the disadvantages of one and the advantages of the other may be secured by using a coil wound upon an iron core whose magnetic circuit is practically closed, excepting for the presence of a small air-gap or interruption in the continuity of the iron core. Such a coil has the advantage that it may be used at all points on the line where current may sometimes be ten and sometimes one hundred milliamperes, whereas if it were of the form in which the reactance wouldvary with the current it would be obvious that the balance for the condenserreactance might be good at some points and bad at others.

In the accompanying drawings, Figure 1 shows asystem of superposed-currenttelegraphy in which my invention may be employed and which has arrangements of receiving and transmitting apparatus devised by me and moreparticularly described and claimed in another application for patent filed by me. Fig. 2 illustrates the application of my invention to a superposed-current telegraph apparatus of modified form. Fig.

The ap- 3 shows the application of my invention to a system wherein the transmitters for the two current.

sides of the system are arranged in another relation to one another and to the circuit.

Referring to Fig. 1, I have shown a number of stations A, B, O, U, V, and WV upon a circuit, each station equipped with pulsatorycurrent and continuous-current apparatus. In practice a very much larger number of stations might be employed,and at intervals on such circuit, if desired, stations equipped with continuous -current apparatus only might be employed, as indicated in Figs. 2

and 3. In the system illustrated in Fig. 1 the continuous-current and pulsatory-current receivers are arranged in shunt relation case is typified by an ordinary Morse receiver adapted to operate after the ordinary manner employed in Morse telegraphs. The receiver for the pulsatory-current side of the system, (indicated at 4,) may be of the ordinary short-core neutral type used in superposedcurrent systems of telegraphy and adaptedto respond to the pulsatory current. The receiver is preferably, however,'of the polarized type in order that it may more readily respond to the action of the pulsatory The relays control the local circuits of receiving instrumentsin the ordinary way.

' In the shunt or branch with the receiver 4 is a condenser 8, employed for the purpose of practically opening the branch in which the receiver4 is placed to the flow of the continubranch having reactance to the pulsatorycurrents, which reactance may be afiorded by the coils of said receiver, and which reactance also operates to force the pulsatory cur-' rents into the condenser branch containing the receiver 4. A non-inductive resistanceshunt 9 is also provided, as described in my application Serial No. 7 9, 385, already referred to, to act as a shu at to the relay 3 and afiord a short-circuiting or diverting pathfor the discharge of the condenser 8, thereby avoiding a kick in the receiver 4. This non-inductive resistance-shunt aids in permitting the pulsa tory currents to flow more freely to stations more distant from the pulsatory-current gen erator. The continuous-current generators, which might be dynamo-machines, are indi cated by thennmeral'5. One of these might be used at each end of the line or section of line, said machines being connected, so that their polarities shall conspire. 6 typifies any pulsa tory-current generator. For a generator in a system employing my present invention I use one adapted to generatea sine-wave electromotive force and prefer to employ an alternating-current dynamo for the purpose. In the system shown in Fig. 1 a pulsatorycurrent generator is provided-at each end of the line. In practice, however, one of them only will be used at a time, that at stationA being shown as in use and as connected to the line through a switching appliance 24, while that at station W is disconnected by switching appliance 24, leaving, however, the

two generators 5 at opposite ends of the line connected to the circuit through switching appliances 25. The transmitter for the continuous-current side ofthe system is shown in this diagram as consisting of the Morse key 2, adapted to open and close a condensershunt around a suitable inductance 12, while the key 1 for the continuous-current-side of the system opens and closes the circuit through said inductance 12,- which latter serves to stop the flow of the pulsatorycurrents over'the circuit during the continuouscurreuttransmission by the key 1.

to one another. The key 2 operates on the pulsatory-current side of the system by cutting the reactance of 12 into and out of the circuit. Each key has its circuit-closer 15 provided with a supplementary contact 16, and said contacts are connected together, so that when both switches are closed the reactanceof the condenser S and inductance12 will be removed from the circuit, and therefore the impedance at way-stations not in use will be so reduced that when the arrangement of receivers shown is employed the system may be worked through a very large number of stations.

In the operation of the system,'as shown, the pulsatory currents employed in transmitting from any station circulateover the whole system and through any apparatus in circuit or not shunted. With the arrangement of devices shown said pulsatory'currents flow through each branch containingacondenser 8 and receiver 4. In the diagram the switch 15 for the continuous-current side of the system at station V is opened and that for the pulsatory-current side at station A. The receivers 3 and 4 maintain their relations tothe circuit at all stations and the pulsatory currents, controlled by transmitter 2 at station A, operate upon the receivers 4 at all stations, the action of the key being simply to open and close the shunt around the inductance 12. Similarly any key at any station may be employed in transmitting signals. In the shunts containing the condenser 8 and receiver 4 the reactance of said condenser isby a suitable construction of the receiver 4 balanced andcounteracted by the counter reactance afforded by the coils ofsaid receiver. The inductance of this coil, the capacity of the condenser, and the frequency of the sine- These keys 1 and 2 are here shown in shunt relation 1 uniform adjustment of the receiving apparaits tus for both sides of thesystem, with little necessity for change of such adjustment, and it will be found that a large number of waystations may be included in the circuit without requiring an extremely high electromotive force'for the pulsatory-current generator employed in the system. Moreover, by the employment of a balancing-inductance the proportion of alternating current which will pass through the continuous-current relay will be very materially reduced, thus making it possible to use a much larger amount of alternating current on the line without disturbing effect upon the continuous-current relay. Theoretically the same result might be accomplished by increasing the size of the condenser; but this is objectionable, because it would be at the expense of the Morse working and add greater cost for equipment.

In the arrangement shown in Fig. 2 the stations A U W are equipped with pulsatory and continuous current apparatus; but the pulsatory-current generators 6 instead of being connected to the circuit and having their pulsations modified by shunting an inductance shunted into and out of circuit arecombined with -a suitable continuity-preserving transmitter 2, adapted'when on its back stop to complete a connection around the pulsatory-current generator 6 and when on the front stop to break the shunt through the pulsatory-currentgenerator into the circuit. Station U is similarly'equipped with a transmitter and pulsatory-current generator, said transmitter and generator holding practically the same relation to the circuit and to an inductance and condenser as does the transmitter 2 in the arrangement shown in Fig. 1.

In Fig. 2 at the terminal stations the transmitter is in a branch from the condenser to ybeing short-circuited to earth. the inductance 12 has the similar function of "earth and the key 1 is in the connection preventing the'current of generator from being short-circuited to earth. Several way- 1 stations B G Vare also shown on the circuit, each being equipped with a continuous-current apparatus, comprisingthe receiver 3 and key 2. The receiver 3 is shunted by the non inductive resistance 9 and by a condenser 8.

The condenser affords a path for the pulsatory currents around the inductance of the receiver 3, and the reactanee of the condenser is balanced by the reactance of an inductance 12, which is of the preferred form already described. The condenser-shunt thus balanced may also extend around the transmitter 1, as indicated. When the circuit-closer 15 for transmitter 1 is closed, it is obvious that there will be present at stations equipped like station E three paths for the current of substantially the same character as that provided bythe receivers in Fig. 1, so that each waystation equipped only with continuous-current apparatus may offer no more impedance to the pulsatory currents than those equipped With apparatus for both sides of the system. The case of the condenser-shunt around the Morse key, station 13, Fig. 2, differs from that 'of the shunt around the relay 3 at station A in that the receiver branch is'always closed,

while the key is sometimes opened. When the Morse key is opened, the only remaining path for the alternating current is throughthe shunt. Sometimes there is no load or retardation coil required in series with the Morse key and in other cases it is required. If'the line has a large number of stations with Morse relays, which are really equivalent to load-coils, and also has smalldistributed capacity, these coils are not required;

.but for the present purpose let us consider a two-station line only where these coils are used. Itis' very objectionable to have the working of the Morse key cause any effect upon the alternating-current relay in the line. It will do this (with a certain adjustment of the relay) if the value of the alternating current flowing is at all disturbed by the opening and closing of the key. For simplification, suppose that there is no line between the terminal stations, but that the circuits have no balancing-coils with the condenser around the keys. If an ammeter is placed in the relay-circuit 4, the alternatingcurrent generator being continuously in the line, the current in 45 will rise when v1 is opened and fall when 1 is closed, the generated eleetromotive force being constant. This result is surprising when first considered, as it is natural to expect that the closing of the key red uces' the total impedance of the line, and thus increases the current in 4. When the proper coils are inserted in the condensershunt around the keys 1, it will be observed that when their inductance is larger than the proper value the current in 4 rises upon closing the key 1 and falls upon opening it.

This is' exactly opposite from the previous effect before the coils were inserted. It is evident, therefore, that there must be some ICC IIO

value for the inductance of the coils, which tained by adjusting until no effect on the alternating current is observed. It wouldbe necessary to resort to vector diagrams, which obtain when sine-waves are employed, to explain this result.

Fig. 3 illustrates my invention as applied to acircuit wherein the balanced condensershunt is employed in connection with the transmitter for the continuous-current side of the system and acondenser-shunt therefor arranged in a relation to the receiver different from that shown in Fig. 2. tions A, B, and W are provided with both pulsatory and continuous-current apparatus. Intermediate stations 0 V are shown provided with apparatus working on the continuouscurrent side of the system only, although a larger number of stations like 0 orlike B might be employed. The transmitters for the pulsatory and continuous current sides of the system are here shown as arranged in series relation to one another instead of shunt relation. Each transmitter 1 for the continuous-current side of the system is adapted to make and break the shunt around a condenser 8, thereby practically opening and closing the circuit for the continuous currents, while each transmitter 2 for the pulsatory-current side of the system operates to make and break a shunt around the inductance 12 of high reactance and low resistance, thereby throwing said reactance into and out of the circuit, so as to alternately permit the pulsatory currents to flow and to stop their flow. This reactance ordinarily being of low ohmic resistance permits the continuous current to flow readily- It is obvious that withthis arrangement of transmitters the pulsatory current must flow through the condenser-shunt 8 around key 1 ance and the reactance of opposite sign pro-- at stations A, B, and WV and similar stations whenever the keyl is opened during the process of transmitting a message by the continuous-current side of the system, and the pulsatory currents must therefore meet the reactance of the condenser S. I therefore in accordance with my present invention provide in the shunt with said condenser an inductance 12 of the character already described and adjust it to balance by its reactduced by the condenser. The resistance of the coil 12 has the additional function of preventing sparking at the contacts of the key 1.

It is obvious that my invention is applicable to other arrangements of the transmitters and receivers for the two sides of the system.

The generator 6 in the foregoing description is to be considered as typical of any source of pulsating currents of sine wave type connected to a circuit in the manner shown and described. It might therefore be the secondary of a transformer the primary of which would include a suitable source of pulsating electromotive force, and also, if desired, a key for closing and breaking the primary circuit, in which case the secondary would be connected directly to the branch In Fig. 3 Sta-- containing the condenser instead of through the points of the transmitter.

The means for producing on the line a pulsatory current of approximately sine-wave form may obviously be of any kind, and, as understood in the art, it might therefore be a source of direct current combined with means for varying the resistance of the circuit for said source. The term pulsatorycurrent generator is therefore to be understood herein as embracing anymeans for producing upon the circuit pulsatory current of the form or approximately the form described.

What I claim as my invention is- 1. In a superposed-current telegraph, the combination substantially as described of a pulsatory-current generator adapted to generate an approximate sinewave electromotive force and condenser shunts or branches around apparatus for the continuous-current side of the system each said shunt having its capacity balanced byinductance, as and for the purpose set forth.

2. In a superposed-current telegraph, the combination with an approximate sine-wave pulsatory-current generator for the pulsatorycurrent side of the system, a transmitter for the continuous-current side of the system a condenser-shunt around the latter and a balancing inductance in said shunt, said inductance, condenser capacity and frequency of pulsations being related to one another as described, as and for the purpose set forth.

3. In a superposed-current telegraph, the combination with a pulsatory-current generator adapted to generate electromotive force of the sine-wave type, a continuous-current receiver and transmitter, and a shunt to the same containing a condenser and inductance related to one another and to the frequency of the pulsations in the manner described to reducethe impedance of said shunt, as and for the purpose set forth.

4. In a superposed-current system of telegraphy, a condenser-shunt containing a receiver for the pulsatory-current side of the system in combination with a pulsatory-cuirent generator of the sine-wave type, the frequency of the pulsations, the reactance of the receiver and the capacity of the condenser being related to one another as described to increasethe strength of current permissible at the transmitting end of the line.

5. A superposed-current system of telegraphy having a sine-wave generator for the pulsatory-current side and shunts around the continuous-current apparatus at way-stations comprising a condenser and balancing-inductance related to one another as and for the purpose described.

, 6. In a superposed-current telegraph, the combination with a pulsatory-current generator adapted to generate an electromotive force of sine-wave type, a continuous-current transmitter and receiver and a shunt around said transmitter'and, receiver containing a TIC netically closed except for the presence of a narrow gap, as and for the purpose set forth.

9. In a superposed-current system of telegraphy, the combination with a condensershunt through which the pulsatory currents flow for operating on the pulsatory-current receiver, of a suitable inductance having a reactance adapted to balance the reactance of said condenser.

Signed at New York city, in the county of New York and State of New York, this 16th day of October, A. D. 1901.

' Y I ALBERT O. OREHORE. \Vitnesses:

J. GALLWITZ,

E. LAVVLER. 

